Method of making rubber articles



-w. c Ross TAL METHOD OF MAKING RUBBER ARTICLES Filed Dec. s, 195s -July s, 1941,.

Patented July 8, 1941 METHOD OF MAKING RUBBER ARTICLES William C. Ross, Winchester, and Earle E. Anderson, Auburndale, Mass. Almy Chemical Com Mass., a corporation o assignors to Dewey and pany, North Cambridge, f Massachusetts Application December 3, 1938, Serial No. 243,792

e claims. (c1. 18.--56) `The present invention contemplates a `method for making lrubberarticles of irregular shape such as gasmasktubes. e H a The difculties which are encountered in the manufacture of irregularly shaped rubber articles by molding mayv n Y to the molding of corrugated rubber gasmask tubes. Not only is it necessary that the moldim'pressionbe accurate, but it is also essential to provide a corrugated wall of uniform thickness and free from cells and cavities su'ch as'are .formed byrkinclusion `ofV air bubbles between the rubber tube and the mold wall. If the wall is not uniform in thickness the tube is Asubject to kinking and pinching with the movements of the wearer, and the air supply may be shut on as a consequence. a Moreover, cells and cavities tend to weaken thew'all of the tube, and to make it porous, areidargerous,` and cannot be tolerated. Accordingly it is an cbject of this invention to provide an improved methodby vwhich articles of irregular shape may be molded with a high degree of accuracy, and by which articles may be made having uniform walls free from air bubblesfMore specifically, it is 'an object of this invention to provide a 'method by which'articles suchas corrugated gas mask tubes may be produced, which are free from air bubbles and other weakening defects of the tube wall; which are characterizedby great uniformity of wall thickness; and which possess thenecessary ilexibility and extensibility. I-Ieretofore, the manufactura ing cost has been greatly increased because of the high percentage of defective tubes. It is another object of this invention to provide an exact dependable, method forI 'producing gas mask tubes, and in which the manufacturing cost will be reduced to a. minimum.

These and other objects will become clear fromv the specification and the drawing in which:

Fig. 1 is a sectional elevational View of a tubular mold for use in forming a tube of gel in ac-` cordance with the invention;

Fig. 2 is a sectional elevational View of a tank used in carrying out one step of the method;

Fig. 3 is a sectional longitudinal View of a tube of latex gel;

Fig. 4 is a similar View of the tube shown in Fig. 3 having its ends closed in preparation for further treatment;

Fig. 5 is a longitudinal sectional View of a mold used for carrying out another step of the method:

Fig. 6 is an enlarged fragmentary sectional view taken upon the line 6-6 of Fig. 5; and

Fig. 7 is a sectional View of another apparatus used in carrying out another step of the method.

In accordance with the invention a hollow article is formed by subjecting an aqueous dispersion of rubber to proper conditions for an appropriate time to produce a gel which is capable be illustrated by reference `243,586 flled December 2, 1938, by William. C.

of plastic flow in the wet gel state. The article is then given the desired final shape by applying pressure to the gel to force it against the inlner 'wall of a hollow mold, thereby bringing about plastic flow of the gel and causing the article to assume the shape of the mold. Pressure may be applied to the gel mechanically. or by filling the gel with a liquid such asvwater, or in any desiredway, but in practice we prefer to carry out the pressure-molding step by inilatingl 'the gel with air under pressure.

In order to avoid air bubbles collecting between the tube and the mold, -it is necessary to lprovide a means for the entrapped air to escape from the` mold. This may be done by forming suitable air vents in the A-denition of the term plastic ow as applied to rubber -gels and a description of the methods by which plastic gels may be produced will be found in copending application S. N.

Ross and Arnolf P. Rehbock.

Briefly, a plastic gel is one which is so soft that it may bepermanently deformed in response to an extraneous force. It may therefore be dis- "tinguished from the tough, elastic gels of the prior art, which set up opposing forces within the gel tending to return the article to its original shape immediately the deforming force is removed. The inflation of hollow articles made fromsuch plastic gelsis characterized by the This phenomenon is designated by the name ous dispersion of rubber takes place. Forexfact that the gel can be inflated to a considerable extent without any rise in internal pressure, i. e. without the development of elastic forces tending to return the article to its original size.

plastic flow. Y

In the above mentioned copending application, asoft or plastic gel is produced by controlling the conditions under which gelation of the aqueample, lthe shorter the gelation time, the softer and more extensible the gel will be. Other variables may likewise be controlled to produce the desired gel properties, for example, temperature vof gelation, and `mass concentration of coagulant in the mix.

We have discovered that such a gel, because itis inelastic and capable of plastic floW, can be forced into exact conformity with the shape of the mold against which it is inflated, Without any tendency to retract or draw away from the mold. Furthermore, since the rubber particles in an expanding soft gel envelope tend to distribute themselves evenly, an accurately Vformed article of uniform wall thickness is produced. Finally, as has been disclosed in the above-mentioned application, the property of plasticity in the gel state inevitably results in high extensibility and flexibility of the finished article.

In .the manufacture of gas mask tubes in accordance with the invention a preform is rst formed in a suitable manner, for example by casting. A suitable compounded latex dispersion containing a dormant coagulant is poured into a tubular mold M (Fig. 1) comprising a tubular wall il! of aluminum which is closed at its ends by detachable caps Il and l2 which also serve to position a core I3 accurately within the mold. The mold is then placed in a tank I5 (Fig. 2) containing Water W at a temperature of'about '71"l C., and allowed to remain in the hot water for about five minutes to cause the dispersion to forma gel preform G (Fig. 3) which isc-apable of plastic ilow in the wet Vgel state.v The mold is then removed from the tank andl chilled in Water atl'l." C-

The preform G is removed `from the mold and plugs IB and I1 are inserted in its ends (Fig. 4') The plug I6 is 'solid and bears an annular flange IB. The -plug l1 also bears anY annular flange i9 and is provided with a passage 20 communieating with the interior of the tube G. The Wall of the passage 2i) is provi-ded with a threaded portiony 2l to receive a compressed air conduit.

IThe preform G having the plugs l5 and l1 inserted inl its ends is lnow positioned in a split hollow mold S (Fig.`5) provided with annular grooves for receiving and retaining the anges i3 andrl). The inner surface of th-e mold Sis provided with corrugations 25, the ribs of which are positioned 'adjacent the Wall ofthe tube Gr.` The adjacent engaging surfaces of the halves ofY the mold S are roughened asl indicated at 21 (Figli) to `provide leakage paths for air which` otherwise would be trapped between the outer surfacev of the gel G and .the inner Wall ofthe mold S. After the halves ofthe mold S` are suitably clamped together a compressed air con-duit Zis connected to the passage 2.and air under a pressure of about 30. pounds per square inch is supplied to theinteiior of the preformG.to cause the latter to be expanded int-othe recesses of the -corrugations .25. As air under pressure is supplied lto ,the interior of thev preform G it causes the latterto expand, and air Vtrapped between the preform G and the inner wallof the mold S is forced through .the paths 21. The air Pressure is `maintained f-or about minutes. .iin

the course of this time plastic flow of the gel takes place, and the wall of gel is forced into intimate contact with the `mold S, forming ar corrugated tube T of gel, the wall of which is ofA great uniformity in thickness.

The removal of water from thegel is usually brought about by synaeresis, which may be accomplished by immersing the gel in Water. In practice, the tube o-f gel T ismounted upon a shaft 30 (Fig. 7) which is mounted for rotation in bearing 3l in the wall of a tank 32 and positioned to permit the `tube Tw to be partly immersed in water 33 in the tank. The tube l is rot-ated'slowly by a driving mechanism 35 so AWe claim:

1. The process of forming a rubber article .which includes making a suitable mixture of an aqueous dispersion of rubber and a gelling agent, converting the mixture into an inelastic gel capable of plastic flow under stress, molding the gel .to final shape by applying pressure to the gel to bring about plastic ilow, and ldrying and vulcanizing the formed gel.

2. The process of forming a corrugated rubber gas mask tube of uniform wall thickness which includes casting a hollow tube of rubber gel of smaller size than the finished tube by lfilling a'mold with :a liquid mixture of an aqueous dispersion of rubber and gelling and vulcanizing agents and heating the mold sufficiently to convert the mixture to an inelastic gel capable of plastic -ow under stress',molding the .tube of rubber gel by applying pressure to its inside surface't-o cause plastic dow of the gel material into intimate contact with the inside surface of a hollow corrugated mold and drying and vulcanizing the gel.

' 3. The process of forming an irregularly shaped hollow article which rincludes inserting in a mold a hollow preform of smaller size than the artcle and `consisting of an inelastic vgel of rubber g material capable of'plast'ic iiow under stress andV moldingthe preform to nal shape by flowing" the gel material 'under pressure'into intimate con-Y tact with ythe mold surface.

4. The process of forming a hollow rubber article from `a liquid latex composition containing a gelling agent including casting an undersize preform by running the composition into a mold and heating the mold until the composition is converted into an inelastic gel capable of plastic' flow under stress, removing the preform from the mold, and form'ing it into final shape by expanding it into a second mold.

5. The process of forming a hollow rubber article from a liquid latex composition contain- X ing a gelling agent, including casting an undersize preform by running the composition into a mold and heating the mold until the composition is converted into an inelastic gel capable of plastic flow under stress, removing .the preform from the mold, forming it into nal shape by flowing the gel material under pressure into intimate contact with a second mol-d, and drying and vulcanizing the gel.

6. The process of forming a hollow irregularly shaped rubber article from a liquid latex composition containing a gelling fag-ent `.which includes forming a hollow preform of smaller size than the finished article by heating the liquid in a preform mold sufciently to convert itinto an inelastic gel 4capable of plastic flowunder stress, removing t'hepreform from the preform mold and molding the preform to'final shape by applying pressure to its interior to cause plastic flow of the gel material.

WILLIAM c. Ross. EARLE` E. ANDERSON. 

